Homework 1 - Myweb @ CW Post

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---! Next, list bonds e-k, in order from most covalent to most ionic. Notice that these are the major elements bonding with oxygen as in silicate minerals. coordination polyhedra & ionic substitution 6)! Using Figures 2.7-2.8 and Table 2.5 in the textbook, determine the coordination number and type for the following ions. ! Note: the values listed in Figs 2.7 & 2.8 are for general use but not necessarily the specific radius in a given compound. The radius listed for Si +4 in b) below is specific for its bonding with oxygen and differs from the general radius given in Fig 2.7. ! a) Na + relative to Cl - in halite (Cl- ionic radius: 1.72 Å) ! b) Si +4 relative to O -2 in silicates (Si +4 ionic radius here is ~0.34 Å; Faure, 1998) ! c) Al +3 relative to O -2 in silicates ! d) Na + relative to O -2 in silicates ! e) Fe +2 relative to O -2 in silicates 7)! Atomic and ionic radii vary with valence state but also with the type and number of surrounding ions (for example, see Table 2.6). Determine the coordination number and type for carbon in carbon dioxide and in carbonate ions: ! a) C +4 relative to O -2 in CO2 (radius of C +4 in CO2: 0.16 Å) ! b) C +4 relative to O -2 in CO3 -2 (radius of C +4 in CO3 -2 : 0.29 Å) ! 8)! Determine whether the following substitutions will occur. Show why or why not, and if coupled substitution is required. Use Figure 2.7 and Table 2.6 for cation radii (note correct coordination in Table 2.6). a) will Mg +2 substitute for Fe +2 bonded to O -2 in silicates ! b) will Ca +2 substitute for Na + bonded to O -2 in silicates ! c) will K + substitute for Na + bonded to O -2 in silicates
9)! The ternary diagram below is Figure 3.3 from p. 48 of the textbook. Plot the compositions of the following two carbonate samples on the diagram (use points A & B from the text as a guide for how to plot). ! ! c) (Fe0.2, Mg0.8)CO3 ! d) (Fe0.8, Mg0.15, Mn0.05)CO3 silicates 10)!Is quartz, SiO2, is electrically neutral or charged. 11)! Determine whether an isolated silica tetrahedron, SiO4, is electrically neutral or charged, and if charged, what its charge is. If charged, how is the charge neutralized 12)!Describe the changing ratio of silicon and oxygen (the formula) in isolated silica tetrahedra, single chains of silica, double chains, silica sheets, and the framework structure of quartz.
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Homework 1 - Myweb @ CW Post

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